1. Field of Invention
The present invention relates generally to ankle foot orthoses (AFOs), and, more particularly, to AFOs which assist in dorsiflexion of the foot.
2. Related Art
Foot drop in a patient can result from several causes. The most common are physical trauma to the tibial nerve, multiple sclerosis, spinal injury and strokes. As a result a person may loose the tone and the ability to contract the dorsal flexors of the foot. This in turn causes a problem termed “foot drop” in which the person points their foot when walking, which results in the person increasing their height of gait in an effort to avoid tripping or dragging their own foot.
The industry has responded to this condition with devices that actively resist plantar flexion. Several early devices utilized a torsion spring in the hinge joint of the AFO. This was only marginally successful, since the joint was large and the spring lost torsion quickly as the foot dorsiflexed.
A more modern device is the Tamarack™ joint developed by Carlson (U.S. Pat. No. D385,358). This device is still widely used today, and is relatively inexpensive to produce, easy to install, and performs successfully in a moderate amount of cases. Nevertheless, it possesses several drawbacks.
For example, in order to use the Tamarack™ joint an AFO must be vacuum-formed specifically for that joint. If it turns out that the patient does not like dorsiflexion assist the AFO can not be changed over to a conventional AFO, and therefore a new AFO must be built. Conversely, patients that have a deteriorating condition, such as MS, may have no need for dorsiflexion assist initially, but in time may deteriorate to a point that need arises in this case; the previously built conventional AFO will need to be discarded and replaced with a new brace incorporating the Tamarack™ joint. This is time consuming and costly. Furthermore, the manner in which the mechanism applies torque is not optimal for treating foot drop: Because the joint relies only on the elongation of the elastic material, as the material stretches the amount of torque exerted through the joint increases more-or-less linearly, i.e., the farther the joint is plantarflexed the more torque it exerts. This is counter to the biomechanics of the foot, since, at a standing position, the calf muscles are not tensed and do not offer much resistance, but as the foot is dorsal-flexed the calf muscles resist due to tension being applied to them through a stretch reflex. However, the Tamarack™ joint rapidly loses tension as the foot is dorsiflexed, and as a result loses the ability to properly dorsiflex the foot. Furthermore, the joint is limited to a peak torque of approximately 2.5 foot/pounds; in many cases this is inadequate to properly dorsiflex the foot, especially with large persons or persons exhibiting spasticity.
The device shown in U.S. Pat. No. 6,752,774 tries to rectify several weaknesses in the Tamarack™ joint. This device addresses the loss in torque by using moment arms to create the torque. This in turn produces torque more uniformly through the range of motion. The device utilizes two hooks over which a small strip of rubber tubing is stretched; as the AFO is plantar-flexed the tubing is stretched and its elasticity creates tension. There are several disadvantages to this ankle joint: It is very large and cumbersome, creating fabrication problem for the orthopedist, and as with the Tamarack™ it requires that the AFO be specifically made for the joint.
The device shown in U.S. Pat. No. 6,602,217 approached this problem using an elastic strap attached at a location proximate the first metatarsal of the foot. This has several problems in that dorsiflexing the foot results in the elastic material rapidly decreasing in length, leading to a rapid fall-off in tension. This decrease in tension is undesirable. Moreover, the path of the elastic material is undesirable as the shoe may interfere with it and render the device unusable.
In summary, existing devices fail to address the biomechanical properties of the ankle joint with proper torque curves. This results in incomplete dorsiflexion and fails to meet the requirements of many individuals, especially those who fall outside the norm. The dorsiflexion assist devices in use today also cannot be incorporated into or adapted to existing AFOs, and therefore require that AFOs be fabricated specifically for their use.
The issues noted above have been discussed in the context of AFOs, but it will be understood that they pertain to dorsiflexion assist devices that are used with night splints as well.
Accordingly, there exists a need for a dorsiflexion assist device for use with ankle foot orthoses and night splints that applies torque in a manner consistent with the biomechanics of the patient's foot. Furthermore, there exists a need for such an apparatus that is adapted to and used with existing AFOs and night splints, so that fabrication of a special AFO or night splint is not required in order to be able to provide dorsiflexion assistance. Still further, there exists a need for such an apparatus that allows the torque characteristics to be adjusted to meet the specific needs of the patient. Still further, there exists a need for such an apparatus that is not bulky and that can be used without interference being caused by a shoe. Still further, there exists a need for such an apparatus that is durable and long-lasting, and that will not lose effectiveness over an extended period of use.